Various particulate filtering media may be formed from diverse materials, such as glass fibers, asbestos fibers, synthetic polymer fibers, e.g., polyolefins, polyamides, polyesters and the like, and natural fibers, such as wood pulp and the like. Desirably, a particulate filter medium should possess a high particulate filtration efficiency, but should also possess a high filtered fluid (e.g., gas or liquid) permeability. However, these performance attributes tend to be inversely related. For example, in some instances, increasing the particulate filtration efficiency of a filter media may tend to increase the pressure differential at the filter media between the filtered fluid and the unfiltered fluid.
As is known in the filtration art, filtration efficiency is improved by improving the ability of the filter media to mechanically entrap contaminates. In some instances, the filter media's ability to mechanically entrap contaminates, such as air born particulates, is improved by increasing the loft or thickness of the filter media without increasing the density of the filter media.
However, increasing the filter media's thickness has several disadvantages. In some instances, existing filter receiving structures may not be large enough to receive such thickened filters. In other instances, and particularly in those instances when the filter media is formed from a conform of wood pulp and polymer fibers, such increased thickness is generally achieved by incorporating increased quantities of the conformed materials. Increasing the quantities of these materials not only results in increased material costs and shipping costs but also reduces the filter material's fluid throughput by increasing the pressure differential across the filter media.
Therefore, there exists a need for a filter media, and particularly for filter media formed from a conform of wood pulp and polymer fibers, and methods of making the same which provides improved filtration efficiencies over conventional filter media formed from similar materials and which avoids the problems associated with conventional methods of improving the filtration efficiencies of filter media.